In an IMT-2000 (International Mobile Telecommunication-2000) system, as shown in FIG. 1, an Iu interface is defined between a RAN (Radio Access Network) node (for example, RNC: Radio Network Controller) and a core node (for example, SGSN: Serving GPRS Service Node), and a GTP (GPRS Tunneling Protocol) tunnel used for transmitting user plane (U-plane) data is set up in the Iu interface.
In the above IMT-2000 system, when a mobile station performs handover across RNCs which are under the control of the same SGSN, that is, when the mobile station performs “SGSN relocation”, the SGSN transmits a “Relocation Request message” by using RANAP (Radio Access Network Application Part), and a GTP tunnel endpoint ID on the SGSN side is reset.
That is, the SGN informs the RNC #2 of a GTP tunnel endpoint ID on the NodeB side by using the “Relocation Request message”, and thereby a GTP tunnel #2 is set up between the SGSN and a handover target RNC #2.
Non-patent Document 1: 3GPP TS25.413